1. Field of the Invention
The present invention relates generally to a color cathode-ray tube with an in-line electron gun and a color cathode-ray tube apparatus using the same.
2. Related Background Art
In a color cathode-ray tube apparatus provided with an in-line electron gun, a horizontal deflection magnetic field and a vertical deflection magnetic field are provided with strong pincushion (FIG. 8) and barrel (FIG. 9) distortions, respectively, for the purpose of self-convergence. The influences accompanying this are found in focus and convergence. In other words, as shown in FIG. 12, the shapes of beam spots, which rightfully should be perfect circles, are distorted due to deflections as follows. In the upper and lower portions of the screen, the shapes of beam spots are horizontally elongated and also are rotated. In the left and right portions of the screen, they are horizontally elongated, wherein the distortion levels are different between side beams, and haze (indicated with broken lines in FIG. 12) is caused due to upward and downward blurs of beam spots. At the diagonal corners of the screen, the beam spots have shapes such as those obtained when the horizontally long shapes are rotated and furthermore, the sizes of haze areas are different between side beams. Any of the above is one of the factors causing the deterioration in image quality. Furthermore, with respect to the convergence, the convergent point of a center beam (G) is different from those of side beams (B, R), which has caused color position shifts (not shown in figures).
In view of such occurrences, conventionally, in order to improve the convergence of three-color beam spots and the shapes of the beam spots in the upper and lower portions of a screen simultaneously, for example, JP 5-36894 B discloses a method in which magnetic pieces are attached to a rear end portion of a deflection yoke and a rear end part of a vertical magnetic field is distorted locally in a pincushion form.
In order to improve the convergence of the center beam relative to that of the side beams in the upper, lower, left and right portions of the screen, for example, JP 57-172636 A and JP 54-146572 A employ a method in which magnetic pieces are provided at an end of an electron gun and the strength of a magnetic field acting on the center beam is varied relative to the strengths of magnetic fields acting on the side beams, thus adjusting the convergence.
In the aforementioned conventional inventions, however, spot distortions in the left and right portions of the screen and the asymmetry in the spot distortions of side beams with respect to each other cannot be corrected, although the convergence of the center beam relative to those of the side beams and the spot shapes in the upper and lower portions of the screen are improved. Thus, the problem of the deterioration in image quality has remained.
This is described with reference to FIG. 11. When beams travel in a direction from the back side to the front side of the paper and are deflected to the right, a pincushion magnetic field is directed upward. In this case, beams B, G and R are subjected to a deflection force and at the same time, a distortion force causing the spot shapes of the beams to be horizontally elongated by a force in a direction perpendicular to that of the magnetic field. Since the beam R is positioned to the right with respect to the beam B, it therefore is subjected to a constant and strong distortion effect, which makes the shape of the beam R horizontally longer, thus causing the asymmetry of the beams B and R with respect to each other, as to the degrees to which their spot shapes are horizontally elongated.
In view of the above-mentioned points, the present invention is intended to provide a color cathode-ray tube and a color cathode-ray tube apparatus that enable focus quality to be improved by generating magnetic fields, on a neck side, with respect to three beams, respectively, for reverse correction of spot distortions to improve the symmetry in the spot distortions of side beams asymmetric with each other.
A first color cathode-ray tube of the present invention includes an in-line electron gun. In the first cathode-ray tube, side beams of three electron beams are allowed to pass through localized barrel magnetic fields formed in a direction substantially perpendicular to an in-line plane and corresponding to the side beams, respectively. Thus, cross-sectional shapers of the side beams are varied so that the cross-sectional shape of one of the side beams is horizontally or vertically elongated to a higher degree than that to which the cross-sectional shape of the other of the side beams is.
According to this, before the electron beams enter a deflection magnetic field, the cross-sectional shapes of the electron beams are varied depending on the asymmetry in the spot shapes of the side beams with respect to each other. Therefore, the nonuniformity in the spot shapes can be improved.
A second color cathode-ray tube of the present invention includes an in-line electron gun. In the second color cathode-ray tube, at the end, on a screen side, of the electron gun, two pairs of members for generating a magnetic field are placed above and below side beams of three electron beams so as to sandwich them, respectively. Between each of the pairs of members for generating a magnetic field, a localized barrel magnetic field is formed to vary cross-sectional shapes of the side beams so that the cross-sectional shape of one of the side beams is horizontally or vertically elongated to a higher degree than that to which the cross-sectional shape of the other of the side beams is.
According to this, the side beams are subjected to the localized barrel magnetic fields before entering a deflection yoke, thus varying the cross-sectional shapes of the side beams.
In the second color cathode-ray tube, it is preferable that the strength of the localized magnetic field formed between each of the pairs of members for generating a magnetic field varies depending on the level of horizontal deflection.
This enables the strengths of the localized barrel magnetic fields affecting the side beams to vary depending on the levels of the distortions of spot shapes.
In the second color cathode-ray tube, it is preferable that the localized magnetic field formed between each of the pairs of members for generating a magnetic field is induced by a horizontal deflection magnetic field generated by the deflection yoke.
According to this, the strengths of the localized barrel magnetic fields affecting the side beams can be varied depending on the level of the horizontal deflection.
In the second color cathode-ray tube, it is preferable that the members for generating a magnetic field have plate-like magnetic bodies placed in planes perpendicular to an in-line direction and parallel to a direction in which the electron beams travel and the plate-like magnetic bodies are positioned in locations shifted inward from planes passing through the central axes of the side beams.
According to this, with a relatively simple configuration, the localized barrel magnetic fields are allowed to act on the side beams. Furthermore, by setting the space between the magnetic bodies to be narrower than that between the side beams, the strengths of the magnetic fields acting on the side beams are allowed to be uneven in cross-sectional planes of the beams and the magnetic fields act on the left and right side beams differently. Therefore, it is possible to vary one of the side beams to have a horizontally elongated cross-sectional shape and the other of the side beams to have a vertically elongated cross-sectional shape.
In the second color cathode-ray tube, it is preferable that ends, on the electron beam side, of the plate-like magnetic bodies are bent and thus planes parallel to the in-line direction are formed.
According to this, areas on which the localized barrel magnetic fields act are broadened, thus improving the effect of correcting the spot distortions.
Furthermore, in the second color cathode-ray tube, it is preferable that the members for generating a magnetic field are four substantially V-shaped magnetic pieces attached to an inner face of a cylindrical body.
According to this, the members for generating a magnetic field can be provided with a relatively simple configuration and therefore can be attached to the end of the electron gun easily.
In the second color cathode-ray tube, it also is preferable that a further pair of members for generating a magnetic field is placed above and below the center beam of the three electron beams so as to sandwich it, thus allowing a localized barrel magnetic field to act on the center beam.
According to this, the magnetic flux density affecting the center beam can be adjusted, thus providing an allowance for the adjustment of convergence.
A third color cathode-ray tube of the present invention includes an in-line electron gun. In the third color cathode-ray tube, at the end, on a screen side, of the electron gun, two pairs of plate-like members are placed above and below side beams of three electron beams so as to sandwich them, respectively. The plate-like members have plate-like magnetic bodies placed in planes perpendicular to an in-line direction and parallel to a direction in which the electron beams travel and the plate-like magnetic bodies are positioned in locations shifted inward from planes passing through the central axes of the side beams.
According to this, with a relatively simple configuration, localized barrel magnetic fields are allowed to act on the side beams. Furthermore, by setting the space between the magnetic bodies to be narrower than that between the side beams, the strengths of the magnetic fields acting on the side beams are allowed to be uneven in cross-sectional planes of the beams and the magnetic fields act on the left and right side beams differently. Therefore, it is possible to vary one of the side beams to have a horizontally elongated cross-sectional shape and the other of the side beams to have a vertically elongated cross-sectional shape. As a result, the nonuniformity in the spot shapes of the side beams can be improved.
In the third color cathode-ray tube, it is preferable that ends, on the electron beam side, of the plate-like magnetic bodies are bent and thus planes parallel to the in-line direction are formed.
According to this, areas on which the localized barrel magnetic fields act are broadened, thus improving the effect of correcting spot distortions.
Furthermore, in the third color cathode-ray tube, it is preferable that the plate-like members are four substantially V-shaped magnetic pieces attached to an inner face of a cylindrical body.
According to this, the members for generating a magnetic field can be provided with a relatively simple configuration and therefore can be attached to the end of the electron gun easily.
In the third color cathode-ray tube, it also is preferable that a further pair of plate-like members is placed above and below the center beam of the three electron beams so as to sandwich it and the plate-like members have plate-like magnetic bodies placed in a plane that is perpendicular to the in-line direction and passes through the central axis of the center beam.
According to this, the magnetic flux density affecting the center beam can be adjusted, thus providing an allowance for the adjustment of convergence.
In addition, a color cathode-ray tube apparatus of the present invention includes any one of the first to third color cathode-ray tubes and a deflection yoke for generating a pincushion-type horizontal deflection magnetic field and a barrel-type vertical deflection magnetic field.
According to this, the symmetry in the spot distortions of the side beams asymmetric with each other is improved, thus providing a color cathode-ray tube apparatus with an improved focus quality.